Method for applying pulsed radio frequency energy to the spinal canal

ABSTRACT

A flexible catheter includes two electrical contacts in a distal region of the catheter and a distal aperture of a hose line. The electrical contacts are connected to a high frequency pulse generator for applying pulsed radio frequency energy for nerve stimulation. A temperature sensor is located in the distal region of the catheter. The flexible catheter is inserted into a region in the spinal canal and the pulsed radio frequency generator is operated, thereby applying pulsed radio frequency energy to a localized region to be treated. The temperature at the distal region of the catheter can also be monitored, and the pulsed radio frequency energy is applied in dependence on the monitored temperature. With the catheter, pain and other medical conditions being related to and influenced by a nervous system are treated.

REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/844,639, filed May 13, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to nerve stimulation by electrically applyinghigh frequency (radio frequency) energy to a localized region of a body.In particular, this invention relates to a flexible catheter or lead fortreatment of a nervous system. More particularly this invention relatesto a flexible epidural catheter and a method for applying pulsed radiofrequency electrical energy to a region in the spinal canal. A fullyimplantable embodiment of the catheter further comprises a transducerbeing adapted to be subcutaneously implanted.

2. Description of Related Art

Catheters are known technical medical products which are manufacturedfor various intended purposes of usage in diagnostics or therapy. Forinstance, epidural catheters are known which can be inserted by aphysician into the epidural space in the region of the spinal canal soas to be able to inject pain-killing drugs, for example. Such a methodis particularly applied in treatment of chronic pain. The catheter canremain in the body for a time period of 1 to 30 days, for example, andthe injection of the drugs can be effected through external or implantedpumps.

Instead of catheters also electrodes are used in therapy of chronicpain. Thus, electrodes for implantation are known, which are connectedto a pulse generator for permanent stimulation of the spinal cord or thenerves. There are also known electrodes for stimulation which areconnected to a transducer that is to be subcutaneously implanted. Inthis case the pulses of the generator are transmitted inductively to thetransducer through the skin of the patient.

Moreover, special needles are known which are connected to a generatorof pulsed high frequency. Such special needles and high frequencygenerators are used to trigger the release of pain-inhibiting substancesin the spinal cord by selectively stimulating nerves, thereby effectinga pain treatment.

However, usage of these rigid special needles is frequently limited dueto anatomical reasons or is avoided because of the risk of injury atintroducing the special needles.

From European patent application EP 1 181 947 A2 an epidural catheter isknown having at least three electrodes arranged in line. The electrodesserve to electrically stimulate nerves or the spinal cord. A channel foradministration of drugs can be provided to allow for injectingpain-killing drugs in addition to the electrical stimulation of thespinal cord.

With the previously mentioned apparatuses operating with electricalstimulation by means of pulses or, in the case of the special needles,by means of pulsed high frequency, control of the effect of thestimulation is solely by feedback from the patient. The mode andintensity of the stimulation is determined on an empirical basis.However, an upper limit of the intensity of the stimulation is given bypossible damage or destruction of the tissue and varies depending on thelocation and the design of the catheter or special needles and on thestructure of the surrounding tissue. Hence, there is no definitecorrelation between the parameters of the applied pulses and the limitwhere damage occurs, so that a margin of safety has to be observed. Thementioned deficiencies also pertain to the documents acknowledged below.

U.S. Pat. No. 4,379,462 to Borkan et al. shows a catheter electrodeassembly for spinal cord stimulation which, unlike the presentinvention, does not include a channel for drug delivery. Frequenciesranging from 10 to 1400 Hz are applied in the stimulation.

International application WO 92/07605 shows an epidural catheterintended to be implanted either temporarily or permanently. In apermanently implantable embodiment, the catheter includes an implantablepulse generator and, at a separate branch of the catheter, animplantable drug reservoir.

U.S. Pat. No. 5,423,877 to Mackey shows a catheter for use in acute painmanagement intended for electrical stimulation of the epidural space ofthe spinal cord. The catheter comprises a conduit for delivery of drugs.The catheter produces a longitudinally elongated electrical field, asleads of the catheter will electrically stimulate a longitudinaldistance of from 10 to 15 cm. However, this is not suitable forselective stimulation of nerves.

U.S. Pat. No. 5,374,285 to Vaiani et al. discloses a spinal electrodecatheter which can be connected to a stimulator.

U.S. Pat. No. 5,081,990 to Deletis shows a catheter for spinal epiduralinjection of drugs and measurement of evoked potentials. Measuringelectrodes located on the tip of the catheter are connected to a voltagedetector. The electrodes are, however, not adapted for electricalstimulation.

German patent application DE 36 02 219 A1 shows a flexible epiduralneuroelectrode comprising a channel with lateral apertures. Theelectrode or catheter allows to administer pharmacological solutionsepidurally and to measure the evoked spinal potentials at the same time(spinal cord monitoring). The electrode is, however, not adapted forelectrical stimulation.

European patent application 1 145 731 A2 shows a multi-lumen,multi-functional catheter system. The catheter system is intended foruse for a therapy of the parenchymal tissues of the brain. Amongst thegenerally mentioned uses is sampling of fluids within the extracellularand interstitial spaces of the brain, spinal cord, or other bodytissues, concurrently with drug delivery or electricalrecording/stimulating. Information gathered by a sensing element ormeasuring device is received by a host computer to evaluate a treatmentprocedure or patient conditions around the locality of treatment. Atreatment procedure would be evaluated either by an operator or byartificial intelligence. Possible sensing systems include thermometricsensing systems. However, unlike the present invention, the applicationEP 1 145 731 A2 does not provide for a flexible epidural catheter havingelectrical contacts for stimulation.

Unlike the present invention, none of the documents described above doesprovide for the usage of high frequency (radio frequency) energy forelectrical nerve stimulation. Also none of these documents describes aflexible catheter comprising a temperature sensor disposed in the distalregion of the catheter. Actually, only the European application EP 1 145731 A2 mentions thermometry at all.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flexible catheterfor treatment of a nervous system, which is suitable for a larger rangeof application than conventional catheters, electrodes or specialneedles, and a method for treatment of a nervous system using saidcatheter.

A further object of the invention is to provide a catheter which isadapted for stimulation with pulsed high frequency.

A further object of the invention is to provide a catheter and a methodfor applying pulsed radio frequency energy to a region in the spinalcanal.

A further object of the invention is to provide a flexible lead fortreatment of a nervous system, which is suitable for a larger range ofapplication than conventional catheters, electrodes or special needles,and a method for treatment of a nervous system using said lead.

A further object of the invention is to provide a method of treatment ofa nervous system for treating a large range of medical conditions.

A further object of the invention is to provide a method of treatment ofa nervous system for treating a large range of organs of the body.

The objects of the present invention are achieved by providing aflexible catheter, particularly a flexible epidural catheter, accordingto the present invention, which comprises at least two electricalcontacts in a distal region of the catheter; leads of the electricalcontacts are located inside the catheter; two of the leads have aconnection for a high frequency pulse generator for nerve stimulation.

In one embodiment, the stimulation catheter for insertion in a body ispart of a stimulation system, the system further comprising an externalcontact; said external contact being adapted to be exposed to anexternal part of said body. With this system, for example, pulsed highfrequency can be applied between said contact in a distal region of thecatheter and said external contact. Moreover, nerve conduction can bemeasured beginning at the nerve root.

When said flexible catheter forms a part of a flexible probe having atleast a second lead and at least a second electrical contact, said radiofrequency energy can be applied between said first and second contacts.Pulsed high frequency can be applied between said two contacts using abipolar signal generator, for example.

A catheter having at least one electrical contact at a distal region issuited for usage with a unipolar pulse generator like, for example, oneof the device N50 of the company Stryker Howmedica, the device RFG-3C+of the company Radionics, and the device Neurotherm of the company RDGMedical.

Preferably, the catheter of the invention is adapted to be inserted intoone of an epidural space, a spinal space, a paravertebral space, anintracerebral region, and regions of ganglia of the head or neck.

Preferably, the catheter is an epidural catheter. When such a catheteris inserted into the region of the spinal canal, it is possible to applya pulsed high frequency current via two electrical contacts to thespinal cord or the spinal nerves instead of or additionally to theinjection of pain-killing drugs, according to requirements. Thus, bystimulating the nerves inside the spinal canal, in many cases atreatment or stimulation of nerve tissue with special needles outsidethe spinal column or in dangerous regions can be avoided, and also thosenerves can be treated with high frequency pulses which otherwise wouldnot have been accessible for this treatment. Thus, the catheteraccording to the invention opens up a distinctly enlarged range ofapplication as compared to a conventional catheter or conventionalneedles.

The catheter enables the stimulation of spinal dorsal nerve rootsproximal to the spinal nerve ganglia with radio frequency and allows toapply pulsed radio frequency (PRF) in the spinal canal and othertargets. New treatments are thus possible. With the catheter and the PRFit is possible to reach vulnerable structures and to treat them with PRFwithout fear of damaging them.

The invention includes providing a method for applying pulsed radiofrequency energy to a region of the spinal canal, this method comprisingthe steps of:

-   -   inserting a flexible epidural catheter into said region, said        catheter having at least two electrical contacts in a distal        region of the catheter;    -   operating a pulsed radio frequency generator; the pulsed radio        frequency generator being coupled to the electrical contacts;        thereby applying pulsed radio frequency energy via said        electrical contacts to at least one of the spinal cord or spinal        nerves;    -   whereby in said region at least one of the spinal cord or spinal        nerves is treated.

In one embodiment, the method further comprises the step of probing aposition of the catheter by applying a test stimulation signal via saidelectrical contacts and thereby probing a sensual response to the teststimulation signal; thereby gaining information about the position ofthe catheter relative to the at least one of spinal nerves and a part ofa spinal cord which is to be treated. Preferably, the test stimulationsignal is applied between two electrical contacts in the distal regionof the catheter, even if the pulsed high frequency energy is appliedbetween one of these contacts and an external contact.

A method for applying pulsed radio frequency energy to at least one of anerve, a nerve root, a nerve ganglion, and a part of a spinal cord in aspace of a spinal canal can be carried out following the steps of:

-   -   inserting a flexible catheter percutaneously into said space,        the catheter having at least one electrical contact at its        distal region;    -   then pushing the catheter forward, thereby positioning said at        least one contact in the spinal canal;    -   adjusting the catheter such that said at least one electrical        contact is in a region of the at least one of a nerve, a nerve        root, a nerve ganglion, and a part of the spinal cord; and    -   operating a pulsed radio frequency generator, thereby applying        pulsed radio frequency energy via the at least one electrical        contact to the region of the at least one of a nerve, a nerve        root, a nerve ganglion, and a part of a spinal cord. Thereby,        the at least one of a nerve, a nerve root, a nerve ganglion, and        a part of a spinal cord is treated.

In one embodiment of this method, the method further comprises a step ofrepeatedly adjusting the catheter to different positions. Thereby,several of nerve roots and parts of the spinal cord can be treated, forexample, one after another, without having to insert the catheter twice.

The invention includes providing a flexible endoscopic probe. Theendoscopic probe comprises at least one electrical contact in a distalregion of the probe, a connection for a high frequency pulse generatorfor nerve stimulation; and at least one electrical conductor runninginside the probe: the conductor connecting said at least one contact tosaid connection. The endoscopic probe allows to position the contactunder endoscopic control and to apply pulsed high frequencyendoscopically. Preferably, the endoscopic probe is compatible tostandard light cables. The endoscopic probe can also be combined withthe catheter to one combined catheter/endoscopic probe for stimulationwith pulsed high frequency. In one embodiment, the endoscopic probe isat least a double lumen probe. One lumen contains an optical conductor,and another lumen contains a lead or the electrical conductor, therebyconstituting a lead.

The same methods as described above can be applied using a lead withouta lumen for transport of liquid instead of the catheter. By inserting aflexible lead into one of an epidural space, spinal space, paravertebralspace, intercerebral region and ganglia of the head and neck, it ispossible to treat at least one of a nerve, a nerve root, a nerveganglion, a part of the spinal cord and a part of the brain, forexample.

The lead can also pass through an endoscopic probe. This allows toposition the lead under endoscopic control and to apply pulsed highfrequency endoscopically.

In one embodiment of the method, the lead further comprises atemperature sensor at the distal region of the lead, leads of thetemperature sensor being located inside the lead, and the method furthercomprises the step of:

-   -   monitoring a temperature using the temperature sensor at the        distal region of the lead;    -   wherein in the step of operating the pulsed radio frequency        generator, the pulsed radio frequency energy is applied        depending in a predetermined way on the monitored temperature.

In another embodiment, the method comprises the steps of:

-   -   displacing the lead to a second localized region; and then    -   repeating the step of operating the pulsed radio frequency        generator;    -   whereby in said second localized region at least one of a nerve,        a nerve root, a nerve ganglion, a part of the spinal cord and a        part of the brain is treated.

Indications and targets for application of pulsed radio frequency withthe invented catheter, lead and method are: pain treatment, diagnosticand therapeutic stimulation, injection of medicaments. All locations inthe spinal canal from the medulla oblongata to the hiatus sacralis canbe treated. In particular, indications and targets are: treatment ofsympathetic and parasympathetic nerves and fibers in vascular diseases,treatment of spasticity, treatment of spastic and motor disorders andpain in: the brain, midbrain, thalamus, hypothalamus, gasserianganglion, cerebellum, medulla oblongata, spinal cord, nerve roots andnerves in the spinal canal, retrograde and direct stimulation of thedorsal root ganglia, dorsal root entry zone (DREZ), stimulation of thedorsal column. For some of these uses, little modifications of thecatheter are needed, as will be apparent to those skilled in the art.

Generally the indication is presently estimated to be at least similarto all indications of the PRF and temperature denervations. In additionfollowing treatments are possible: radicular diseases as the postherpetic neuropathy, mono- or polyneuropathies, complex regional painsyndrome (CRPS), neuralgia, ischaemic disease, pain, spasticity andmotor disorders.

Generally, the pulse radio frequency energy may be applied to alocalized region for treatment of a medical condition that is related toand influenced by at least one of a nerve, a nerve root, a nerveganglion, a part of the spinal cord and a part of the brain, which istreated in said localized region. That is, the medical condition to betreated, for example a disease, may be affected, controlled, modified orcaused by the central or peripheral nervous system. One example of sucha medical condition is a neurogenic disorder.

Medical conditions that are related to a nerve, a part of a nerve or ofthe central of peripheral nervous system include indications and targetsthat have been mentioned above. For example, the medical condition maybe pain, for example chronic pain, neuralgia, and the complex regionalpain syndrome (CRPS).

Other medical conditions are those that are related to a nervousdisorder or a neuro-muscular disorder, such as radicular diseases andmono- and polyneuropathies.

The medical condition may be also a movement disorder or a motordisorder, for example, spasticity and spastic and motor disorders.

Further medical conditions that are related to and influenced by acentral or peripheral nervous system are vascular diseases andcirculatory disorders, for example, ischemec disease.

Although one of the main benefits of the application of pulsed radiofrequency is treating neuropathic pain, it has been found that the leadand the catheter of the invention are also advantageous in treatingpatients with other diseases having a connection to the nerve system.Amongst these diseases are cases where pain is not the main symptom.

The central or peripheral nervous system can cause or modify manyconditions. It has been found that treating the spinal cord or thedorsal roots or other nerves with pulsed radio frequency can interferewith the diseases which are maintained by these nerves.

In one embodiment of the method of the invention, the pulsed radiofrequency energy is applied to the localized region for treatment of amedical condition that is related to and influenced by the at least oneof a nerve, a nerve root, a nerve ganglion, a part of the spinal cordand a part of the brain, wherein the medical condition is connected withan organ of the body that is associated with the at least one of anerve, a nerve root, a nerve ganglion, a part of the spinal cord and apart of the brain.

For example, the medical condition is at least one of:

-   -   disorders of bladder function,    -   disorders of micturition,    -   disorders of bladder sensation,    -   disorders of detrusor functions,    -   neuropathic bladder,    -   urinary incontinence,    -   detrusor-sphincter dyssynergia, and other sphincter        dysfunctions,    -   disturbances of micturition due to disorders of the central        nervous system,    -   disorders due to spinal cord injury,    -   disorders due to spinal cord diseases,    -   idiopathic bladder disease, idiopathic sphincter disease,    -   disorders of erection and ejaculation,    -   interstitial cystitis and other visceral pain syndroms,    -   central and peripheral vascular diseases,    -   anal pruritus, and    -   fecal incontinence.

Preferably, the pulsed radio frequency energy is applied to thelocalized region for treatment of an organ of the body that isinnervated by the at least one of a nerve, a nerve root, a nerveganglion, a part of the spinal cord and a part of the brain.

In another embodiment of the method of the invention, the pulsed radiofrequency energy is applied to the localized region for increasing theblood circulation in a part of the body, said part of the body beingassociated with the at least one of a nerve, a nerve root, a nerveganglion, the part of the spinal cord and a part of the brain. Thereby,a dilatation of peripheral blood vessels or hyperemia may be effected.

Preferably, the catheter of the invention further comprises a distalaperture of at least one hose line being located between two of thecontacts. Such an arrangement allows to treat the same area with drugsas well as with high frequency stimulation without having to alter thelocation of the catheter. Moreover, due to the proximity of the contactsto the distal aperture of the catheter, the advantage results thatduring insertion of the catheter, the location of the catheter can beprobed via a test stimulation with reduced voltage and frequency. Thus,stimulation can serve to localize the pain or the pain conductingnerves, and in this manner, a preferably well suited position for thecatheter can be found. Another advantage is that the x-ray contrast ofthe contacts is sufficiently high to allow positioning of the catheterwith x-ray monitoring without application of a contrast agent.

Preferably, the contacts of the catheter are disposed in a row along thelongitudinal direction of the catheter. Preferably, the catheter ends atits distal end with a contact the outer surface of which has the shapeof a cap. At least one of the contacts preferably has an outer surfacehaving the shape of an annular strip encircling the catheter.

Preferably, the catheter is also connectable to pulse generators beingapplicable for permanent stimulation of nerves.

Several possible and advantageous configurations of the catheter areconceivable. For example, the leads of the contacts can be disposedwithin a hollow space of the catheter which is separated from the innerspace of each hose line. The leads of the contacts can also run withinthe wall of the catheter. The catheter can also comprise a hose line inthe form of a tube disposed within the catheter and, for example,filling a hollow space of the catheter.

Preferably, the outer diameter of the catheter is less or equal 1.67 mm,more preferably 1.33 mm, and the catheter preferably has a length of atleast about 60 cm. Preferably, the contacts are disposed one afteranother at a distance of a few millimeters along the longitudinaldirection of the catheter. Preferably, said distance is 4 mm.

In an embodiment of the invention, the catheter further comprises atemperature sensor in the distal region of the catheter; leads of thetemperature sensor are located inside the catheter.

Thus, with the catheter further comprising a temperature sensor at thedistal region of the catheter, leads of the temperature sensor beinglocated inside the catheter, a method as described above can be carriedout, the method further comprising the step of monitoring a temperatureusing the temperature sensor at the distal region of the catheter,wherein in the step of operating the pulsed radio frequency generator,the pulsed radio frequency energy is applied depending in apredetermined way on the monitored temperature.

For example, at least one parameter of the pulse generation isautomatically changed when a specific temperature has been reached.

When the epidural catheter comprising the temperature sensor is insertedinto the area of the spinal canal, and a pulsed high frequency currentis applied to the spinal cord or the spinal nerves via two contacts, anincrease of temperature caused by the stimulation or effected by theapplied electrical energy can be monitored by means of the temperaturesensor. For example, a temperature monitoring circuit or device can beprovided which automatically switches off or temporarily suppresses thestimulation when an upper temperature limit of 42° C. is reached so asto avoid thermal damaging of the tissue.

By monitoring the tissue's temperature using a temperature sensor,nerves or the spinal cord can be treated with pulses or pulsed highfrequency the parameters of which can be varied within larger boundarieswithout having to worry about thermally damaging the tissue. Thus it ispossible to optimally adapt the intensity of the stimulation to theneeds of the patient, especially when using pulsed high frequency whichis high in energy. Such frequency can also be used with frequentlyrepeated stimulation or permanent stimulation over a longer time,because an accumulated rise of temperature can reliably be monitored.Even if the electrical parameters of the tissue change due to adsorptionof tissue or modification of the local tissue structure, and more energyis introduced due to a higher conductive loss, damaging can be avoidedbecause of the temperature monitoring. Thus, the invented catheter opensup a still larger range of application compared to a conventionalstimulation catheter.

Preferably, the temperature sensor is a thermocouple, for instance ofthe type nickel-chromium/nickel. The advantage of a thermocouple is thatits thermal voltage is independent of the geometry of the point ofcontact of the two leads. Moreover, the thermocouple can be manufacturedwith very thin wires having an accordingly low thermal inertia,resulting in immediate detection of an increase of temperature. Since athermocouple is an active sensor, conducting resistance isunproblematic. The leads of the temperature sensor can be the wires ofthe thermocouple.

Preferably, the temperature sensor is thermally connected to one of theelectrical contacts. In this way, the temperature can be measureddirectly at the heated spot, and a good thermal contact is achieved.

One of the connecting leads of the temperature sensor can also serve asa lead of one of the electrical contacts. Thereby, one lead is saved.

The leads of the contacts and/or the connecting leads of the temperaturesensor can be disposed within a hollow space of the catheter which isseparated from the inner space of each hose line. The leads of thecontacts and/or the connecting leads of the temperature sensor can alsorun within the wall of the catheter.

In another embodiment the catheter comprises a transducer; theelectrical contacts are connected via the leads to the transducer, andthe transducer is adapted to be subcutaneously implanted and is adaptedto transmit high frequency pulses for nerve stimulation onto the leads;the catheter further comprises a port in a proximal area of thecatheter; the port is adapted to be subcutaneously implanted.Preferably, the catheter is an epidural catheter.

After insertion of the catheter, the catheter can be completelyimplanted, including the transducer and the port, beneath the skin nearto the point of entrance into the body. When later using the catheterfor stimulation of the spinal cord or of nerves, for example, the riskof infection is reduced due to the closed skin and the risk ofcomplications is reduced. Moreover, the catheter being concealed belowthe skin is easier to handle for the patient.

When such a catheter is inserted as an epidural catheter into the areaof the spinal canal, for example, in addition to stimulation of thespinal cord or the spinal nerves by means of a pulsed high frequencycurrent, injection of a pain-killing drug via the port can take place,according to requirements. The implanted port can, for example, beconfigured in form of a septum, which can be reached from external andpierced with a injection needle.

Thus, this embodiment of the catheter has further distinct advantages ofusage over a conventional catheter and thereby opens up an even furtherrange of application.

Optionally, between the port and the catheter, a drug pump can beprovided being likewise implantable. Thereby, an evenly distributeddispensing of drugs is achievable over a longer time period.

Optionally, the transducer comprises a device for storing energy. Thisdevice can effect the energy supply of a drug pump, for example.

The high frequency pulses can be transmitted inductively from anexternal device to the transducer, for example. Alternatively, energycan be supplied inductively to the transducer, and the transducer itselfgenerates the pulses for nerve stimulation.

The transducer can also comprise a pulse generator for stimulation orpermanent stimulation of nerves.

Preferably, the transducer comprises a coil. In particular, the coil canbe a coil for sending and receiving. Thus the coil being utilized forsending, the catheter is adapted to send signals to a device outside thebody.

Preferably, the catheter further comprises a temperature sensor in thedistal region of the catheter, and leads of the temperature sensor arelocated inside the catheter. The feature of the temperature sensor andadvantageous applications have been described above in detail.Preferably, the transducer is adapted to receive a signal effected bythe temperature sensor.

For monitoring the temperature the transducer can send signals to anexternal device, and a monitoring circuit can be provided externally ordisposed within the transducer, said monitoring circuit automaticallyswitching off or temporarily suppressing the stimulation when an uppertemperature limit of 42° C., for example, has been reached, so thatthermal damaging of the tissue can be avoided.

Preferably, the transducer is adapted to receive an electrical signalfrom the electrical contacts. Thereby, a measurement of an excitationpotential of a nerve can take place, for example.

In a preferred embodiment the catheter further comprises an injectionchamber for the catheter being located at the port. Thereby, theinjection of drugs via the port is facilitated and the injection chambercan also serve as a reservoir chamber for an implantable drug pump.

In a preferred embodiment, the transducer and the port are disposed in aflat casing being subcutaneously implantable. The combination of theport and the transducer in one casing facilitates locating them in casea drug is to be injected into the catheter, for example. Furthermore,the casing can accommodate the coil of the transducer, for example, andcan serve as a supporting surface for the injection chamber or for theport, thus facilitating the handling when introducing an injectionneedle into the port.

All embodiments of the catheter or lead mentioned above can be implantedto remain in the body for a period of, for example, up to several daysor weeks. In this way, high frequency pulses can be applied at severaltimes.

Further scope of the applicability of the present invention will becomeapparent from the detailed description of preferred embodiments of theinvention given hereinafter. However, it is to be understood that thedetailed description and the specific examples, while indicatingpreferred embodiments of the invention, are given by way of illustrationonly, since various changes and modifications within the spirit andscope of the invention will become apparent to those skilled in the artfrom this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only and thus are not limiting ofthe present invention and wherein

FIG. 1 is a schematic view of an epidural catheter having two contacts,a thermocouple, and a hose line;

FIG. 2 is a schematic longitudinal sectional view of a tip of a firstembodiment of an epidural catheter;

FIG. 3 is a transverse sectional view of the catheter of FIG. 2:

FIGS. 4 and 5 show a second embodiment of a catheter in viewscorresponding to FIGS. 2 and 3;

FIGS. 6 and 7 show a third embodiment of a catheter in viewscorresponding to FIGS. 2 and 3;

FIG. 8 is a schematic view of an embodiment of an epidural catheterhaving a transducer with a coil within a flat casing beingsubcutaneously implantable, as well as an external device having anantenna;

FIG. 9 is another view of the casing and the transducer with the coil;

FIG. 10 is a schematic view of a stimulation lead passing through anendoscopic probe; the lead having one electrical contact and athermocouple;

FIG. 11 is a cross-sectional anatomical view of a spinal cord in aspinal column; and

FIG. 12 is a sectional view of a spine taken along the length of thespine;

For reasons of clarity, the drawings are not drawn to scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an epidural catheter 10 comprising in its distal region adistal contact 12 and a proximal contact 14 between which a lateralaperture 16 of a hose line 18 is disposed. Contacts 12 and 14 are drawnwith hatching. The distal contact 12 forms a cap encasing the end of thecatheter 10. The proximal contact 14 forms an annular strip encirclingthe catheter 10. The edges of the contacts 12 and 14 are flush with amantle 20 of the catheter 10 made of silicone rubber.

The outer diameter of the mantle 20 is 1.33 mm, corresponding to aspecification of 4 French. In longitudinal direction of the catheter 10the contacts 12 and 14 extend to a length approximately corresponding tothe outer diameter of the mantle 20. The contacts 12 and 14 are offsetto each other by approximately 4 mm in longitudinal direction of thecatheter 10. The overall length of the shown epidural catheter 10 is 60cm, however, other lengths are also conceivable.

Within the catheter 10, a thermocouple 21 (FIG. 2) is thermallyconnected to the distal contact 12. Electrical leads 22 for theelectrical contacts 12, 14 as well as connecting wires 23 and 24 of thethermocouple 21 run within the mantle 20 parallel to hose line 18 andare, like hose line 18, indicated with dashed lines in FIG. 1.Thermocouple 21 is of the type nickel-chromium/nickel, wire 23 being ofnickel-chromium and wire 24 being of nickel. The internal configurationof catheter 10 will be further explained below with FIGS. 2 and 3.

Catheter 10 comprises a fixation device 25 which can serve to fasten thecatheter to a point where the catheter enters a body, the element 25being configured like in a conventional implantable catheter.Furthermore, in a known manner an aseptic guide wire (not shown) isdisposed within the hose line that serves to push the catheter 10 to thedesired position in the spinal canal and is then retreated. The guidewire is slightly bendable in the region of its leading end.

At a connecting member 26, the electrical leads 22 are led out of themantle 20 of catheter 10 in form of electrically isolated wires 28, andwires 23 and 24 are led out of the mantle 20 into an isolated cord 29.The hose line 18 continues within a mantle 30, which is a continuationof mantle 20, to a connector 32. Said connector serves for connecting asyringe or a drug pump and is configured in a conventional manner.Between the connector 32 and connecting member 26 is disposed a clip 34that allows to clamp hose line 18 and re-open it by releasing clip 34.The clip 34 is configured in a conventional manner, as well, and canalso be disposed at the connection 32.

Wires 28 are provided with electrical connectors 36 and 38. Connector 36is connected to the distal contact 12, and a connector 38 is connectedto the proximal contact 14 of the catheter. Connectors 36 and 38 aremerely schematically shown in the drawing, and can be encoded in termsof color and/or in terms of the shape of contacts of the connectors.Said connectors are adapted to be directly or via an adapter (not shown)connected to a pulse generator 39 generating a pulsed high frequencycurrent. The pulse generator 39 can, for example, be the device N50 ofthe company Stryker Howmedica, the device RFG-3C+ of the companyRadionics, or the device Neurotherm of the company RDG Medical.

The connectors 36, 38, wires 28, leads 22, and the contacts 12 and 14are adapted both for application of pulses for a test stimulation ofnerves or of a spinal cord having, for example, a voltage in the rangeof 0 to 12 V, a frequency in the range of 50 to 150 Hz, and a pulsewidth in the range of 150 to 400 microseconds, as well as for applyingpulsed high frequency, for example, within a voltage ranging from 20 to30 V and a pulsed frequency of 500 kHz and a pulse width of 20 ms. Thenumerical values given are only examples to illustrate the range ofapplication of the catheter.

A bipolar connector 40 of cord 29, being secured against connecting withthe wrong polarity, is connected to the wires 23 and 24 of thethermocouple 21. Connector 40 is adapted for connecting to a measuringdevice 41, which measures the temperature in the region of the distalcontact 12 of the catheter using the thermocouple 21.

The measuring device 41 can be integrated into the pulse generator 39 inform of an appropriate circuit, for example, or can be connected to thepulse generator, so as to automatically effect a switching off or achange of parameters of pulse generation when a specific temperature isreached; said specific temperature being adjustable. For example, anadaptive or stepwise control of pulse generation can be provided thatreduces the power and/or frequency of the pulses when an intended uppertemperature limit is approached. Alternatively or, if the temperature istoo high, additionally the pulse generation can be temporarily stoppeduntil a sufficiently low temperature is reached again.

FIG. 2 shows the tip of the catheter 10 of FIG. 1 as a longitudinalsectional view, though the catheter 10 as well as the leads 22 and wires23, 24 disposed in front of and behind the plane of the drawing areshown in a sectional view.

The electrical leads 22 and wires 23, 24 each comprise an isolation 42.Leads 22 are internally soldered to the distal contact 12 and theproximal contact 14 respectively. The thermocouple 21 is formed by acontact point of the nickel-chromium wire 23 and the nickel wire 24 andis connected to the contact 12 via the wire 23 in immediate proximity.Thus, a good heat conduction between the contact 12 and the thermocouple21 is accomplished.

The mantle 20 of the catheter 10 comprises an internal partition wall 44dividing the inside of the catheter 10 into a first hollow space formingthe hose line 18 and a second hollow space 46. The leads 22 and wires23, 24 run within this second hollow space 46. The electrical contacts12 and 14 are separated from the hose line 18 by the mantle 20. Thelateral aperture 16 of the mantle 20 opens the hose line 18 to theoutside.

FIG. 3 shows a cross-sectional view of the catheter 10 along the lineIII-III of FIG. 2. The arrangement of leads 22 and wires 23, 24 withinthe second hollow space 46 of the mantle 20 is shown.

FIGS. 4 and 5 show a second embodiment, wherein the mantle 20 has nointernal partition wall 44 forming a second hollow space 46. Instead theelectrical leads 22 and the wires 23, 24 with their respectiveisolations 42 run within a thickened area of the wall of the mantle 20of the catheter 10. The hose line 18 is formed inside the mantle 20 in away similar to the first embodiment.

FIGS. 6 and 7 show a third embodiment which differs from the secondembodiment in that inside the mantle 20, there is an additional internaltubular layer 48 forming the hose line 18. The mantle 20 encloses thetube formed by the internal layer 48 as well as the isolations 42 of theelectrical leads 22 and wires 23, 24. At least at the aperture 16, whichpenetrates the layer 48 and the mantle 20, the internal layer 48 istightly connected to the mantle 20. However, the internal layer 48 canalso be a part of a mantle of the catheter constituted of two or morelayers.

The tube formed by the inner layer 48 ends on the other side of theaperture 16. It can, however, also extend into the cap formed by thedistal contact 12 as indicated by chain dotted lines. The internal layer48 is isolated by the mantle 20 from the contacts 12 and 14.

The shown embodiments are meant to demonstrate a possible arrangementand contacting of the electrical leads 22 and of the thermocouple 21 andits wires 23, 24 and to present possible constructions of the hose line18. It is to be understood that the catheter of the invention can alsohave a configuration that differs from these embodiments, for example acombination of the inner layer 48 of FIG. 7 with the two hollow spacesof the mantle 20 of FIG. 3, or a different location of the thermocouple21.

Alternatively, the electrical contact 12 can also be configured havingthe shape of an annular strip. It goes without saying that more than thetwo shown contacts can be provided.

FIGS. 8 and 9 show another embodiment of the catheter 10 the distal partof which is constituted similar to the catheter of the third embodimentshown in FIGS. 6 and 7.

As the proximal end of the catheter 10, the catheter is seamlesslyconnected to a flat casing 52. The upper region of the casing 52contains an injection chamber 54 which is connected to the hose line 18.The upper wall of the injection chamber 24 comprises a bulge forming aport 56 in form of an injection septum. Via the port 26, the injectionchamber of the implanted catheter is accessible from external by way ofan injection needle, for example. The injection septum is made in aknown manner such that its wall is sufficiently dense and elastic so asto provide a reliable sealing after an injection needle previouslyinserted through the septum is retracted.

In the lower region of the casing 52 a coil 58 is arranged spirally, ascan be seen more clearly in FIG. 9. The coil 58 is a sending andreceiving coil and is connected to a transducer 60. The transducer 60has several functions which will be explained hereinafter.

At the casing, an aperture for introducing the guide wire is closedbefore implanting the casing.

The electrical leads 22 and the wires 23, 24 are connected to thetransducer 60. The transducer is adapted to measure currents and/orvoltages. For example, the transducer 60 can measure a thermovoltage onthe wires 23 and 24 of the thermocouple, thereby monitoring thetemperature at the distal end of the catheter 10. The transducer 60 canalso measure potentials between the electrical contacts 12 and 14, forexample. Such potentials can provide information about the excitationcondition of nerve roots or the spinal cord, for example.

The transducer 60 is addressed by an external device 70 comprising anantenna 72 cooperating with the sending and receiving coil 58 of thetransducer 60. The pulse generator 39 and indication devices 76 areconnectable to the external device 70.

The pulse generator 39 produces a pulsed high frequency current. Thehigh frequency pulses are inductively transmitted by the antenna 72 tothe coil 58 and are relayed by the transducer 60 to the leads 22 of theelectrical contacts 12 and 14. The contacts 12 and 14, the leads 22, andthe transducer 60 and the coil 58 are adapted both for application ofpulses for a test stimulation of nerves or of a spinal cord having, forexample, a voltage in the range of 0 to 12 V, a frequency in the rangeof 50 to 150 Hz, and a pulse width in the range of 150 to 400microseconds, as well as for applying pulsed high frequency, forexample, within a voltage ranging from 20 to 30 V and a pulsed frequencyof 500 kHz and a pulse width of 20 ms. The numerical values given areonly examples to illustrate the range of application of the catheter.

During pauses in-between the pulses and at times where no stimulationtakes place, the transducer 60 can send signals via the coil 58 to theexternal device 70, which receives the signals by means of its antenna72. Information can be transmitted concerning the temperature measuredby the temperature sensor as well as information concerning electricalsignals the transducer 60 receives from the electrical contacts 12 and14. Furthermore, further signals can be transmitted from the transducer60 to the external device 70 or in the opposite direction for controlpurposes, for example. The indication devices 76 can display measuredvoltages, currents or temperatures.

In case the transducer 60 detects that an allowable maximum temperatureof the temperature sensor 21 is exceeded, the transducer 60 can effectan automatic switching off or changing of parameters of pulse generationof the pulse generator 39 by means of control signals, for example.Thus, an adaptive or stepwise control of pulse generation can beprovided that reduces the power and/or frequency of the pulses when anintended upper temperature limit is approached. Alternatively or, if thetemperature is too high, additionally the pulse generation can betemporarily stopped until a sufficiently low temperature is reachedagain.

FIG. 9 shows the casing 52 of the catheter 10 of FIG. 8 as viewed fromthe bottom of FIG. 8. The spiral configuration of the coil 58 isvisible.

FIG. 10 shows an endoscopic probe 80 with a light conductor 82 thatcontains optical fibers for light delivery and visualization, as isknown in the art. However, the endoscopic probe 80 also comprises astimulation lead 84 having a distal electrical contact 12 in the distalregion of the probe 80. The light conductor 82 ends at the distal end ofthe probe 80.

The endoscopic probe 80 and the stimulation lead 84 are configuredsimilar to the catheter 10 of FIG. 1, the major difference being thatthe hose line 18 is replaced by the light conductor 82. Therefore,similar parts are numbered with the same numbers as in FIG. 1, and therespective parts of the description of the catheter of FIG. 1 areincluded herein by reference. Another difference to the catheter 10 ofFIG. 1 is that the stimulation lead 84 has only one contact 12 in itsdistal region. This contact 12 is connected to the connector 36. Asecond, external contact 86 is connected via a wire 88 to the connector38.

Contact 12 forms an annular strip encircling the probe 80. Athermocouple is thermally connected to the contact 12. At the connectingmember 26, the light conductor 82 continues within a light cable 90 thatis compatible to standard light cables for endoscopy and ends at aconnector 92.

FIG. 11 shows a sectional view of a spinal cord 100 and a spinal columnat a level of a vertebra 102. Dorsal roots 104 and ventral roots 106 aswell as spinal ganglia 108 of spinal nerves 110 are indicated. Withinthe spinal canal, an epidural space 112 is shown into which the catheter10 is to be inserted.

FIG. 12 schematically shows insertion of the partially shown catheter 10into the spine. For example, the catheter 10 can be placed at themedullary conus 114 and cauda equina 116. The 12th thoracic vertebra118, the 5th lumbar vertebra 120 and the 1st sacral vertebra 122 areindicated.

The catheter 10 can be inserted in a similar manner as conventionalspinal cord stimulation (SCS) electrodes. A guide wire (mandrel) is usedto steer the catheter in place and can be bent. The procedure is as easyas the placement of an SCS.

The inventor found out that it is plausible to place the catheter at theconus 114 and cauda equina 116. Here the nerve roots converge and can betreated by the passing catheter 10 one by one. Thus, the catheter is,for example, inserted at the contralateral or ipsilateral side into themid-line of epidural space 112 or laterally and pushed obliquelyupwards, passing the dorsal roots 104 of the spinal nerves 110. Thecatheter 10 is usually inserted under local or general anesthesiapercutaneously through a Tuhoy needle by the loss of resistancetechnique into the epidural space 112. The catheter 10 is then pushedforward in an oblique way to lie at the dorso-lateral wall of the spinalcanal.

The point of insertion of course depends on the nerves intended totreat. If, for example, it is intended to treat the lumbar nerves thecatheter is introduced at the L2/3 space, as indicated in FIG. 12,pushing it up to the Th. 12 level, thus enabling to stimulate the nervesTh12 up to L 5. Or if it is intended to stimulate the sacral nerves thecatheter has to be inserted at a deeper level L3/4, as indicated with adashed line, pushing it up to the level L1. Then it is possible to treatthe entire lumbar roots in addition to all sacral roots.

To be sure which nerves are affected they can be identified bystimulation with a frequency of 80 Hz, for example. The response of thepatient is an accurate indication for the distances of the tip to thedesired nerve.

After inserting and pushing upwards the catheter 10, at first the mostcranial nerve root is stimulated and there, the PRF application isperformed. Then, while stimulating, the catheter 10 is slowly retrieved.The sensations diminish and then when reaching the next nerve root riseagain. There, the next PRF application is started. This procedure isrepeated until all nerve roots positioned in the course of the catheterhave been treated. The temperature sensor at the tip allows to becontinuously informed about the temperatures at the tip.

The catheter 10 can be left in place up to 30 days. The procedures canbe repeated at the same or any other level. It is also possible to addthe catheter to an implantable device to repeat the PRF application atany time, as described herein before.

The catheter 10 is cannulated and allows to inject fluids, like steroidsand other substances used in adhesiolysis, if desired. Medicaments canbe injected as in any other catheter. Thus, it is possible to stimulatethe dorsal nerve roots and ganglia proximal to the spinal ganglia and toapply PRF.

Especially when dealing with several segments and in difficultanatomical structures this flexible catheter is easier and safer to use.There are at least one ore more contacts at the tip of the catheter. Thedistal contact applies PRF and stimulation with all possiblefrequencies. This enables a very accurate positioning of the tip.Adapters can be provided for to connect the catheter to any radiofrequency generator.

If intended for research, nerve conduction can be measured.

The catheter allows direct application of pulsed radio frequency toneural structures in the skull, the epidural space and in the spinalcanal. This was until today impossible. It largely extends the use ofradio frequency which was limited by using thermo-lesion needles outsideof the epidural space, the spinal cord or canal. It is safer than heatand can be applied directly to the spinal cord. A permanent temperaturecontrol at the top of the catheter makes the procedure safe.

Adhesiolysis and the injection of steroids are possible. Exact placementby stimulation is another benefit of the catheter. The new obliqueapplication technique could be of great therapeutic value.

With the catheter or lead of the invention, pulsed radio frequency maybe applied for treatment of a medical condition that is related to andinfluenced by the central or peripheral nervous system. The indicationsand targets for application of pulsed radio frequency which have beenmentioned above are confirmed by the following example of the treatmentof a patient that suffered from a neurogenic bladder.

The female patient, born 1934, had a disk herniation at the L4/5position in 1979. She suffered from a severe urinary retention due to aneurogenic bladder. The residual urine capacity was about 1000 ml. Thepatient could only void 50 ml spontaneously. In spite of severalmedication her problem could not be solved. A complete urologicalexamination came to the conclusion that there was no possible cureexcept a conventional operation.

Then, in May 2004, the catheter was introduced via the sacral hiatus,and the S 2 to S 4 roots were stimulated by pulsed radio frequency.

Since that date slowly the conditions got better. The spontaneous urinewas once 720 ml (03.11.2004) and once 580 ml (04.11.2004).

In addition to a nearly normalization of the conditions the patient wasable to feel her urge to void from the first day on after thestimulation, which was a feeling she had missed for many years. At leastthis was described as a great improvement by the patient.

Furthermore, by the application of pulsed radio frequency according tothe invention, a dilatation of peripheral blood vessels or hyperemia maybe effected. This has been confirmed by the treatment of patients withpulsed radio frequency applied through the catheter of the invention.The patients felt a hyperemia in their feet, and a dilatation of theirperipheral blood vessels was recognized.

The given examples also confirm that an organ being associated with orinnervated by a part of a central or peripheral nervous system may betreated according to the invention.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Furthermore, all the disclosed elements andfeatures of each disclosed embodiment of the catheter, stimulationsystem, lead, endoscopic probe or method can be combined with, orsubstituted for, the disclosed elements and features of every otherdisclosed embodiment of the catheter or method, respectively, exceptwhere such elements or features are mutually exclusive. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention, and all such modifications as would be obvious to one skilledin the art are intended to be included within the scope of the followingclaims.

What is claimed is:
 1. A method for applying pulsed radio frequencyenergy to a region in the spinal canal, comprising the steps of:inserting a flexible epidural catheter into a spinal space, saidcatheter having at least one first electrical contact in a distal regionof the catheter and a distal aperture of at least one hose line;injecting pain killing drugs to a localized region to be treated via thedistal aperture of the at least one hose line; operating a pulsed radiofrequency generator, the pulsed radio frequency generator being coupledto said first electrical contact; thereby applying pulsed radiofrequency energy via said first electrical contact to the localizedregion to be treated; detecting a temperature in the spinal space by atemperature sensor at the distal region of the catheter; andautomatically changing at least one parameter of the pulsed radiofrequency energy supplied to the localized region when a specifictemperature is detected, automatically switching off or temporarilysuppressing of the pulsed radio frequency energy to the localized regionwhen an upper temperature limit of 42° C. is reached to thereby avoidthermal damage of tissue, whereby in said localized region at least oneof a nerve, a nerve root, a nerve ganglion and a part of the spinal cordis treated.
 2. A method as claimed in claim 1, wherein the pulsed radiofrequency energy is applied to said localized region for treatment of amedical condition.
 3. A method as claimed in claim 1, further comprisingthe step of probing a position of the catheter by applying a teststimulation via said electrical contact to detect a sensual response tothe test stimulation signal.
 4. A method as claimed in claim 3, whereinthe test stimulation signal has a voltage in the range of 0 to 12 V, afrequency in the range of 50 to 150 Hz, and a pulse width in the rangeof 150 to 400 microseconds.
 5. A method as claimed in claim 1, furthercomprising the step of repeatedly adjusting the catheter to differentpositions.
 6. A method as claimed in claim 1, wherein the step ofdetecting the temperature comprises using a temperature sensor that isthermally connected to the first electrical contact.
 7. A method asclaimed in claim 1, wherein the step of inserting the flexible epiduralcatheter into the spinal canal comprises disposing an aseptic guide wirewithin the hose line, pushing the catheter to the desired position inthe spinal canal, and retreating the guide wire.
 8. A method as claimedin claim 1, wherein the step of injecting pain killing drugs uses asyringe or a drug pump.
 9. A method as claimed in claim 1, wherein theapplied pulsed radio frequency energy has a voltage in the range of 20to 30 V, a frequency of 500 kHz and a pulse width of 20 ms.